Alzheimer's disease is a neurodegenerative disease caused by accumulation of a causative substance such as β-amyloid in brain, causing damage to nerve cells. Although the number of patients suffering from Alzheimer's disease is expected to increase upon the advent of an aging society, prophylactic agents and therapeutic agents for the disease are hardly available, and development of new prophylactic agents, therapeutic agents, vaccines and the like has been demanded.
The major amyloid β proteins produced in the brain of Alzheimer's disease patients are composed of 40 to 43 amino acids produced by cleavage of amyloid precursor protein with γ-secretase. Amyloid plaques are aggregates constituted by amyloid β and surrounding microglia, fibrous astroglia and dystrophic neurites. The most commonly accepted hypothesis at present on the pathology of Alzheimer's disease is the “amyloid cascade hypothesis”, in which formation of amyloid plaques due to aggregation and deposition of amyloid β is considered to be the cause. Based on this hypothesis, the vaccine immunotherapy is drawing attention as a novel therapeutic method for Alzheimer's disease. The vaccine immunotherapy is a method to remove amyloid β in the brain by an immunological method, and it has been reported that intramuscular administration of amyloid β42 to disease model transgenic mice together with an adjuvant caused decrease in the amount of deposition of amyloid in the brain (WO 99/27944; Schenk D. et al, Nature 400:173-177, 1999).
Further, although an anti-amyloid β antibody that recognizes amyloid has been detected in the serum of a subject to whom a synthetic amyloid β42 was intramuscularly administered together with an adjuvant, side effects such as meningoencephalitis have been problematic in clinical trials (Hock C. et al., Nat. Med. 8:1270-1275, 2002).
Therefore, vaccine compositions for prophylaxis and/or therapy of Alzheimer's disease, which are free from side effects, are demanded.